III/V semiconductor materials, such as, for example, III-nitrides (e.g., indium gallium nitride (InGaN)), III-arsenides (e.g., indium gallium arsenide (InGaAs)), and III-phosphides (e.g., indium gallium phosphide (InGaP)), may be employed in various electronic, optical, and optoelectronic devices. Examples of such devices include switching structures (e.g., transistors, etc.), light-emitting structures (e.g., light-emitting diodes, laser diodes, etc.), and light-receiving structures (e.g., waveguides, splitters, mixers, photodiodes, solar cells, solar subcells etc.). Such devices containing III/V semiconductor materials may be used in a wide variety of applications. For example, such devices are often used to produce electromagnetic radiation (e.g., visible light) at one or more wavelengths. The electromagnetic radiation emitted by such devices may be utilized in, for example, media storage and retrieval applications, communications applications, printing applications, spectroscopy applications, biological agent detection applications, and image projection applications.
III/V semiconductor materials may be fabricated by depositing, or “growing,” a layer of III/V semiconductor material on an underlying substrate. The layer of III/V semiconductor material, which is crystalline, may be substantially comprised of a single crystal of the III/V semiconductor material. The substrate is selected to have a crystal structure like that of the III/V semiconductor material to be grown thereon. The substrate may have a known, selected crystallographic orientation, such that the growth surface of the substrate on which the III/V semiconductor material is to be grown comprises a known crystallographic plane in the crystal structure of the substrate material. The crystalline III/V semiconductor material having a crystal structure like that of the substrate material then may be grown epitaxially on the underlying substrate. In other words, the crystal structure of the III/V semiconductor material may be aligned and oriented with the similar crystal structure of the underlying substrate. Although the crystal structure of the III/V semiconductor material may be similar to that of the underlying substrate, the spacing between the atoms in a given crystallographic plane within the crystal structure of the III/V semiconductor material may differ (in the relaxed, equilibrium state) from the spacing between the atoms in the corresponding crystallographic plane within the crystal structure of the underlying substrate. In other words, the relaxed lattice parameter of the III/V semiconductor material may differ from the relaxed lattice parameter of the underlying substrate material.
In greater detail, the III/V semiconductor material layer may initially grow “pseudomorphically” on the underlying substrate, such that the actual lattice parameter of the III/V semiconductor material is forced (e.g., by atomic forces) to substantially match the actual lattice parameter of the underlying substrate upon which it is grown. The lattice mismatch between the III/V semiconductor material and the underlying substrate may induce strain in the crystal lattice of the III/V semiconductor material, and the strain results in corresponding stress within the III/V semiconductor material. The stress energy stored within the III/V semiconductor material may increase as the thickness of the layer of the III/V semiconductor material grown over the substrate increases. If the layer of III/V semiconductor material is grown to a total thickness equivalent to, or beyond, a thickness commonly referred to as the “critical thickness,” the III/V semiconductor material may undergo strain relaxation. Strain relaxation in the III/V semiconductor material may deteriorate the crystalline quality of the III/V semiconductor material. For example, defects such as dislocations may foam in the crystal structure of the III/V semiconductor material, the exposed major surface of the layer of III/V semiconductor material may be roughened, and/or phases may segregate within the otherwise homogenous material, such that regions of inhomogeneity are observed within the layer of III/V semiconductor material.
In some cases, these defects in the III/V semiconductor material may render the III/V semiconductor material unsuitable for use in the ultimate operational device to be formed using the III/V semiconductor material. For example, such defects may result in electrical shorting across a P-N junction formed in such a III/V semiconductor material as part of a light-emitting diode (LED) or a laser diode, such that the P-N junction and the diode do not generate the desired electromagnetic radiation.
There is a need in the art for methods of forming III/V semiconductor materials that have smaller and/or reduced numbers of defects therein, and for semiconductor structures and devices that include such III/V semiconductor materials having smaller and/or reduced numbers of defects.